1. Field of the Invention
The present invention relates to an inorganic thin film polarizer. More specifically, the present invention relates to an inorganic thin film polarizer having improved resistances against heat and weathering. The thin film polarizer comprises a matrix for the polarizer which is made of an inorganic material and composed of columns, and light absorbing portions formed on the surface thereof.
2. Description of the Related Art
Polarizers constitute one of the fields of advanced materials now placed under active R & D. For example, sheet polarizers are used in combination with liquid crystals and are incorporated in thin LCD's (Liquid Crystal Displays) which are now widely utilized in liquid crystal display devices of compact calculators and wrist watches, taking their advantage of low electric power consumption, low voltage drive, thin body, and large display area. To this end, the application field of the LCD's is expanding with the progress in the field of electronics, and the LCD's are replacing the CRT displays conventionally used in TV sets and in display devices of personal computers and word processors. Furthermore, their application is now intensively developed, for example, to depolarization plates and circular polarizers, three-dimensional image processing (e.g., X-ray and motion pictures), OA (office automation) machines, polarizer lens, partial detectors, glare shields, dimmers, and the field of cameras.
Since a polarizer transmits the light whose electric vector is parallel to one of the principal axes, i.e. "polarizing axis", while absorbs or scatters the light when the electric vector of the incident light is perpendicular to the polarizing axis, the sheet polarizer has a function to select a linear polarized light from a unpolarized light or to extinct the light whose electric vector is not parallel to the polarizing axis.
The conventional sheet polarizers have been produced by: stretching an organic material such as polyvinyl alcohol (PVA) and polyvinyl chloride (PVC); adsorbing iodine or dyes, which is dichroic molecule, in the stretched sheet or by dehydrating or dechlorinating PVA or PVC, to thereby give dichroism to the sheet; and thereafter laminating or coating both sides of the sheet having dichroism with the layers of a matrix (e.g., triacetyl cellulose, polyethylene terephthalate, and polymethyl methacrylate). However, the conventional sheet polarizers composed mainly of organic materials are disadvantageous in that they are liable to decompose or deteriorate under ultraviolet (UV) light, heat, moisture, or certain types of organic solvents. Moreover, they also suffer poor mechanical strength. Since the sheet polarizers are provided in film sheets, their assembly into a display device and the like requires additional manufacturing steps of cutting and laminating. It is another problem that such sheet polarizers have difficulty in applying them to products having complicated or curved shapes, or to those particularly small in size.
As a method for overcoming the problems mentioned hereinbefore, there is proposed a "Process for Producing Polarizers" as disclosed in Japanese Unexamined Patent Publication No. 54-143658. The process as disclosed therein comprises steps of: depositing a planar layer of an electrically conductive material on a glass substrate at a deposition angle of 90.degree., and irradiating a particle beam to the deposition layer at a proper angle of incidence to thereby provide a plurality of fine etched bands running parallel to each other. In this manner, a polarizer comprising a plurality of electric conductive bands arranged in parallel to each other at a grid spacing of about one tenth of the wavelength of light can be produced on the glass substrate. The disclosure teaches that this process enables production of low cost polarizers having a long life and good reproducibility. However, the polarizers obtained by this process comprises an electric conductive substance such as a metal in the light absorbing portion, and the structure is such that this light absorbing portion is exposed on the surface of the polarizer. Since electric conductive substances such as metal are generally soft and are thereby inferior in abrasion resistance, conventional polarizers required a protective film to compensate for the insufficient abrasion resistance. The irradiation of a particle beam onto the surface of the polarizer inevitably requires use of a glass substrate, and this makes it difficult to produce flexible polarizers as compared with the organic film polarizers. Furthermore, the irradiation of particle beams arranged in one direction over a large area is also difficult to achieve in this conventional process for producing polarizers. Hence, large scaled polarizers have not been feasible with the conventional process.